<?php
$s="How are you?";
echo "[$s]\n";
echo  "[",trim($s),"]\n";
$s="how are you?";
echo strpos($s,"o"),"\n";
echo strpos($s,"o"),"\n";
$pos=0;
echo $pos=strpos($s,"0",$pos),"\n";
echo $pos=strpos($s,"o",++$pos),"\n";
$a="计算机123";
echo  bin2hex($a),"\n";
echo  hex2bin("e8aea1e7ae97e69cba313233"),"\n";
echo chunk_split("123456",2,":"),"\n";
echo chunk_split("e8aea1e7ae97e69cba313233",2,":"),"\n";
echo chunk_split("e8aea1e7ae97e69cba313233",2,"_"),"\n";
$s="How old are you?";
echo str_replace('o','**',$s),"\n";
echo str_replace(['o','r'],"*",$s),"\n";
echo str_replace(['o','r'],['O','R'],$s),"\n";
print_r(str_replace(['o','r'],['O','R'],[$s,'hero']));
 echo str_replace(' ','',$s),"\n";
echo join(', ',[123,456,789]),"\n";
echo join(', ',[123,456,789]),"\n";
echo strtolower('How are you.\n');
echo strtoupper('I m fine ,Thank you.\n');
echo strtoupper('e8_ae_a1_e7_ae_97_e6_9c_ba_31_32_33_\n');
$s='hello world!';
printf('[%s] [%1$.5s] [%1$8.5s] [%1$ -8.5s]\n',$s);
var_dump(str_starts_with('hell','ll'));
var_dump(str_starts_with('Hell','He'));
var_dump(str_starts_with('Hell','he'));